To meet the demand for wireless data traffic, which has increased since deployment of 4th-generation (4G) communication systems, efforts have been made to develop an improved 5th-generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘beyond 4G network’ or a ‘post long-term evolution (LTE) system’.
It is considered that the 5G communication system will be implemented in millimeter wave (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To reduce propagation loss of radio waves and increase a transmission distance, a beam forming technique, a massive multiple-input multiple-output (MIMO) technique, a full dimensional MIMO (FD-MIMO) technique, an array antenna technique, an analog beam forming technique, and a large scale antenna technique are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, a device-to-device (D2D) communication, a wireless backhaul, a moving network, a cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation, and the like.
In the 5G system, a hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) modulation (FQAM) and a sliding window superposition coding (SWSC) as an advanced coding modulation (ACM) scheme, and a filter bank multi carrier (FBMC) scheme, a non-orthogonal multiple access (NOMA) scheme, and a sparse code multiple access (SCMA) scheme as an advanced access technology have been developed.
Firstly, various channel codes have been used in a communication system, and a typical one is a low density parity check (LDPC) code.
The LDPC code is an error correction code of which an encoding and decoding complexity is really implementable and a performance approaches a theoretical channel capacity. The LDPC code may be designed thereby being suitable for parallel processing and an error correction performance of the LDPC code on a channel is good, so the LDPC code has been used in various communication systems such as an institute of electrical and electronics engineers (IEEE) 802.11n/ad Wi-Fi communication system, an IEEE 802.16e worldwide interoperability for microwave access (WiMAX) communication system, a digital video broadcasting-satellite-second generation (DVB-S2) communication system which is based on a second generation DVB-S2 standard, a DVB-terrestrial-second generation (DVB-T2) communication system which is based on a second generation DVB-T2 standard, a DVB-cable-second generation (DVB-C2) communication system which is based on a second generation DVB-C2 standard, an advanced television system committee (ATSC) 3.0 communication system which is based on an ATSC 3.0 standard, a G.hn communication system which is based on a G.hn standard as a home network standard, and/or the like.
Meanwhile, a binary LDPC code may be defined based on a parity check matrix including elements which have a value ‘1’ and elements which have a value ‘0’. The number of rows and the number of columns included in the parity check matrix may be expressed as N and M, respectively. In a case that the LDPC code which may be defined based on the parity check matrix is used, message bits of a length K are generated as codeword bits of a length N. Here, K=N−M.
The LDPC code is a typical block code. The block code is generally designed thereby supporting a one fixed code rate. If necessary, a signal transmitting apparatus performs a puncturing operation on a codeword generated based on an LDPC code supporting the one fixed code rate to acquire a target code rate. In a case that the signal transmitting apparatus generates a codeword by performing a simple puncturing operation to adjust a code rate, a performance of the generated codeword is significantly degraded compared to a codeword generated based on an LDPC code designed thereby being suitable for an original code rate.
If a communication system needs to maintain a performance and support various code rates, it may be a simple solution to directly design and use LDPC codes suitable for the code rates which the communication system needs to support. However, it may be a significant hardware load to a signal transmitting apparatus and a signal receiving apparatus to design all of LDPC codes of which the number is equal to the number of code rates which the communication system needs to support, to store parity check matrixes which correspond to the designed LDPC codes, and to use the parity check matrixes.
Study for a rate compatible (RC)-LDPC code for solving this issue has been continuously progressed by various study groups. The RC-LDPC code is an LDPC code which may support various code rates with one structure. Upon using the RC-LDPC code, a signal transmitting apparatus may effectively generate codewords for supporting various code rates through a puncturing operation. The signal transmitting apparatus may support an incremental redundancy-hybrid automatic retransmission request (IR-HARQ) scheme using this RC-LDPC code.
In a case that an RC-LDPC code is designed, an LDPC code with the highest code rate is fixed, and an LDPC code with a low code rate is repetitively generated. The lower a code rate is, the more degraded a performance of a codeword generated based on an RC-LDPC code is.
However, RC-LDPC codes proposed up to now are designed for supporting various code rates without considering performance degradation of a codeword due to decrease of a code rate.
The performance degradation of the codeword due to decrease of the code rate as described above in a communication system supporting an RC-LDPC code degrades total system performance. That is, the RC-LDPC code may not provide a good performance for all code rates, so a link adaptation scheme which is based on the RC-LDPC code may not provide a good performance. A performance of an IR-HARQ scheme is significantly affected by a performance of a code rate applied to initial transmission which is based on channel quality, the RC-LDPC code may not provide a good performance for all code rates, so a performance of an IR-HARQ scheme is also degraded when the RC-LDPC code is used.
As described above, in a case that an RC-LDPC code is used, a good performance may not be guaranteed for all code rates. Due to this, total system performance and stability of a communication system are degraded.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.